Traditionally, coil components such as inductors, transformers, and chokes are used in a wide variety of applications such as home electric appliances, industrial apparatuses, and vehicles. A coil component is composed of a magnetic core and a coil wound around the magnetic core. Such a magnetic core often includes ferrite, which is superior in magnetic properties, freedom of shape, and cost.
In recent years, as a result of downsizing of power supplies for electronic devices, there has been a strong demand for compact low-profile coil components operable even with a large current, and magnetic cores produced with a metallic magnetic powder, which has a saturation magnetic flux density higher than that of ferrite, are increasingly used for such coil components. Such a metallic magnetic powder includes, for example, a magnetic alloy powder such as an Fe—Si alloy powder or an Fe—Ni alloy powder. Although having high saturation magnetic flux density, magnetic cores obtained through the compaction of the magnetic alloy powder compact have low electrical resistivity due to the use of the alloy powder. Therefore, the magnetic alloy powder to be used is provided with an insulating coating in advance. For this problem, there is proposed a technique for imparting insulting properties to a magnetic core by oxidizing soft magnetic alloy particles including iron, silicon, and an element more vulnerable to oxidation than iron (such as chromium or aluminum) to form an oxide layer on the surface of the particles (see Patent Document 1).
It is also known that when produced with Fe—Si—Al alloy particles, magnetic cores can have reduced iron loss. Since the Fe—Si—Al alloy particles are relatively hard and low in deformability (formability), magnetic cores produced with such particles tend to have more voids between the particles and to have lower magnetic permeability. Thus, there is proposed a technique for increasing magnetic permeability by using Fe—Si—Al alloy particles in combination with highly-compressible Fe—Ni alloy particles, in which these particles are provided with an insulating coating in advance, respectively (see Patent Document 2).